Deonte Martinez turned himself in Thursday morning at Chula Vista police headquarters.. Photo via Chula Vista Police Department

A third suspect was arrested Thursday in connection with the fatal shooting two weeks ago of a 17-year-old boy at a South Bay park, authorities reported.

Deonte Martinez, 22, allegedly was one of two assailants who opened fire on the teen during a brawl at Sunset View Park in the Eastlake area of Chula Vista on the evening of March 11, according to police.

Patrol officers responding to reports of gunfire shortly before 7:30 p.m. found the victim, whose name has not been released, on the ground, mortally wounded. Paramedics took him to a hospital, where he was pronounced dead.

“The investigation has shown the victim went to the park prior to the shooting with several acquaintances,” said Lt. Dan Peak. “While at the park, a physical fight took place between the group(s). After the fight, two subjects brandished handguns and began shooting the victim. The reason for the fight and motive for the shooting remains unknown.”

On Monday, detectives arrested a young man and a juvenile on suspicion of taking part in the deadly altercation. Larry Bradford, 18, and the 16-year-old boy were taken into custody at a home in Spring Valley, Peak said.

The minor, whose name was withheld because he is underage, was booked into juvenile hall on suspicion of murder. Bradford was jailed on an accessory- to-murder charge.

Martinez turned himself in through his attorney late Thursday morning at Chula Vista police headquarters.

“The investigation is still ongoing but has been able to determine Martinez also shot the victim during the incident,” the lieutenant alleged.

Peak said police have declined to publicly identify the victim because he was a minor at the time of his death.